Bronze-based alloy of low lead content

ABSTRACT

The object of the present invention is to provide a bronze-based alloy of low lead content, first improved in tensile strength at high temperatures, secondly contributing to the promotion of the environmental conservation including recycling, while avoiding the adverse effect of lead on human bodies by means of reduction of a lead content, and excellent from the standpoints of mass-productivity and manufacturing cost. The alloy includes 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %&lt;P≦0.6 mass % and the remainder of Cu and unavoidable impurities to improve the tensile strength thereof at high temperatures.

TECHNICAL FIELD

The present invention relates to a bronze-based alloy of low lead content suitable as a material for plumbing instruments, such as valves or joints for water supply, hot water supply or steam emission, pressure instruments, such as cylinders or casings, or structural members and particularly to a bronze-based alloy of low lead content improved in tensile strength at high temperatures and capable of contributing to the soundness of a casting.

BACKGROUND ART

A bronze casting (JIS H5120 CAC406) is generally excellent in castability, corrosion resistance, machinability and pressure resistance and has numerously been used for plumbing instruments for water supply, hot water supply and steam emission, such as valves, cocks and joints. The bronze casting (CAC406) contains several % of Pb (lead) and contributes particularly to the enhancement of machinability and pressure resistance. In recent years, however, it has been recognized that even low-concentration Pb might adversely affect human bodies, resulting in trends toward the establishment of regulations in various fields over the world, such as regulations for the leaching of Pb into tap water, discharge of Pb-containing waste and content of Pb in a material to be used. Under these circumstances, there has been an urgent need to anew develop useful leadless copper alloys. Of these alloys, various materials including Bi-based, Bi—Sb-based and Bi—Se-based alloys have been developed.

For example, JP-B HEI 5-63536 (Patent Document 1) discloses a leadless copper alloy substituting Bi for lead to enable the enhancement of cuttability and the prevention of dezincification. In Japanese Patent No. 2889829 (Patent Document 2), disclosed is a leadless bronze to which Sb is added to enable the suppression of the generation of porosities during the course of casting in consequence of the addition of Pb for enhancing the cuttability, thereby achieving the enhancement thereof in mechanical strength. In addition, U.S. Pat. No. 5,614,038 (Patent Document 3) discloses a bronze alloy having Se and Bi added thereto to particularly deposit a Zn—Se compound thereon, thereby making the mechanical properties, cuttability and castability thereof substantially identical with those of CAC406.

[Patent Document 1] JP-B HEI 5-63536

[Patent Document 2] Japanese Patent No. 2889829

[Patent Document 3] U.S. Pat. No. 5,614,038

DISCLOSURE OF THE INVENTION Problems the Invention Intends to Solve

In the leadless bronze casting having Bi added thereto as a substitute component for Pb, as in the above Patent Documents, where it contains a slight amount of Pb, when the casting material has been exposed to such a high temperature as exceeding 1000° C., among other mechanical properties the tensile strength is possibly lowered. It is conceivable as one of the causes thereof that Bi and Pb exist as Bi—Pb binary eutectic crystals of low melting point in the crystal grain boundaries and in the crystal grains where portions fragile at high temperatures are formed. There is the same trend toward the generation of these phenomena in various materials having Bi added thereto, such as Bi-based, Bi—Sb-based and Bi—Se-based materials.

The applicant of this application proposed in the previously filed application No. PCT/JP2004/4757 the technique of having Te contained in an alloy to materialize the enhancement of mechanical properties at high temperatures. However, since a bronze casting used for valves for steam emission etc. is required to have a prescribed tensile strength even at a high temperature of approximately 180° C., a further improvement in tensile strength at high temperatures and in mass-productivity by dint of use of more numbers of general-purpose alloy components has been desired.

As the technique of suppressing the production of Bi—Pb binary eutectic crystals and improving the tensile strength at high temperatures, a technique of super reduction making the Pb content approximate to zero is conceivable. In major cases, however, conventional casting equipment for producing CAC406 is used concurrently for the mass-production of leadless copper alloys and, in such a case, there is a possibility of interfusion of Pb from a furnace and a ladle. In addition, since leadless copper alloys are produced using recycled materials, such as scraps, or ingots comprising such recycled materials and since these materials contain Pb mixed therein as an unavoidable impurity, even when the casting equipment exclusive for producing leadless copper alloys is used, it is unavoidable that Pb be mixed in the leadless copper alloys. Under the present set of circumstances, therefore, the content of Pb up to 0.25 mass % is allowable (for leadless bronze valves prescribed under JIS B 2011). Thus, the technique of super reduction making the Pb content approximate to zero is impractical from the standpoints of mass-production and manufacturing cost.

Here, as regards the tensile strength of ordinary bronze-based alloys at high temperatures, though it is recognized that sand castings made of bronze-based alloy has exhibited a decrease in tensile strength at high temperatures, the experience shows that the continuously cast castings (about 28 mm in diameter) shown in Table 1 exhibit no decrease in tensile strength at high temperatures in the approximate range of 100° C. to 200° C. (refer to FIG. 21: cited from “Industrial Technology of Leadless Copper Alloy Castings and Their Applied Instances,” The Materials Process Technology Center, published Oct. 15, 2004, pp. 35 an 37) However, there is no material quantitatively grasping these phenomena over other casting diameters or casting processes (Example: metal mold casting).

TABLE 1 Chemical component value (mass %) Sample Cu Bi Zn Sn Sb Pb AQ05 Balance 0.50 6.50 4.36 0.10 0.06 AQ10 Balance 0.88 6.61 4.29 0.10 0.05 AQ15 Balance 1.43 6.98 4.55 0.11 0.09 AQ20 Balance 1.96 6.86 4.40 0.11 0.08 AQ30 Balance 2.66 6.80 4.33 0.12 0.07 CAC406C Balance — 5.27 4.35 5.48

The present invention has been developed as the result of keep studies made in view of the aforementioned problems and has as its object to first improve the tensile strength of a bronze-base alloy of low lead content at high temperatures, secondly provide a bronze-based alloy of low lead content excellent in mass production while avoiding the adverse effect of lead on human bodies owing to the reduction in the amount of lead and contributing to the promotion of the environmental conservation including recycling and further to secure the soundness of castings.

Means for Solving the Problems

To attain the above object, the invention set forth in claim 1 is directed to a bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass % and the remainder of Cu and unavoidable impurities, whereby the P increases grain boundary strength in the alloy to improve tensile strength thereof at high temperatures.

The invention set forth in claim 2 is directed to a bronze-based alloy of low lead, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass %, 0.0 mass %<Ni≦3.0 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures and secure soundness of a casting.

The invention set forth in claim 3 is directed to a bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass %, 0.0 mass %<Se≦1.3 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures and secure soundness of a casting.

The invention set forth in claim 4 is directed to a bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass %, 0.0 mass %<Ni≦3.0 mass %, 0.0 mass %<Se≦1.3 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures and secure soundness of a casting.

The invention set forth in claim 5 or claim 6 is directed to a bronze-based alloy of low lead content, further comprising 0.005 to 2.0 mass % of Pb to secure a tensile strength of at least 152 MPa at a temperature of 180° C. in an alloy region having a secondary dendrite spacing of 14 μm or more.

The invention set forth in claim 7 is directed to a bronze-based alloy of low lead content used as a material for a valve, water faucet clasp or water meter.

Effects of the Invention

According to the invention of claim 1, it has been made possible to provide a bronze-based alloy of low lead content, improved in tensile strength at high temperatures, contributing to the promotion of the environmental conservation including recycling and excellent from the standpoints of mass-productivity and manufacturing cost. The application of the conventional leadless copper alloys has been limited to implements for the supply of water or hot water having a principal temperature of 100° C. or less in use. However, the copper alloy of the present invention improved in tensile strength at high temperatures can be developed to appropriate use of the conventional bronze alloys over the general application, with no restriction made on its application, and can enlarge the range of its application as recycled materials and exhibits its effects from the viewpoints of the manufacturing cost, not to mention the environmental conservation. In particular, it is preferably applicable to alloys low in cooling velocity during the course of casting, such as sand castings, and optimum for alloys requiring a tensile strength of 152 MPa at a high temperature (about 180° C.).

According to the invention of claim 2, it has been made possible to provide a bronze-based alloy of low lead content, suppressing a decrease in tensile strength at high temperatures, contributing to the promotion of the environmental conservation including recycling and excellent from the standpoint of mass-productivity. In addition, it contains Ni as a principal component to obtain P—Ni interaction, thereby suppressing the content of P therein, enabling the tensile strength thereof to be 152 MPa at a high temperature (about 180° C.) and obtaining the action of enhancing the tensile strength thereof by means of the Ni using the content of 0 mass %<P≦0.6 mass %. While, in the “pressure container structure” under JIS B 8270, the fundamental allowable stress of CAC 406-2 at 200° C. is prescribed at 38 MPa, the present invention makes it possible to secure even at high temperatures 152 MPa that is four times the prescribed value. While the excess content of P in a casting has a tendency to lowering the soundness of the casting, the P—Ni interaction enables the tensile strength at high temperatures to be secured even in a small content of P, thereby also securing the soundness of the casting to a satisfactory extent. Thus, it is possible to obtain an alloy suitably usable for a pressure-resistant container, such as a valve.

According to the invention of claim 3, it has been made possible to provide a bronze-based alloy of low lead content, containing Se as a principal component, suppressing the content of Bi and exhibiting its tensile strength of 152 MPa at a high temperature (about 180° C.). Since Se is present in the alloy in the form of intermetallic compounds of Se—Zn and Cu—Se, it is effective for securing the tensile strength and soundness of a casting while suppressing the content of Bi. Thus, it is possible to obtain an alloy suitably usable for a pressure-resistant container, such as a valve.

According to the invention of claim 4, it has been made possible to provide a bronze-based alloy of low lead content, containing Ni as a principal component to suppress the contents of P and Bi and exhibiting its tensile strength of 152 MPa at a high temperature (about 180° C.).

According to the invention of claim 5, it is made possible to provide a bronze-based alloy of low lead content, which can secure an excellent tensile strength even at high temperatures without being affected by the content of Pb. As a result, the tensile strength at high temperatures can be secured without being affected by Pb interfused from a furnace and a ladle in the case where the conventional casting equipment for producing CAC406 is used concurrently for the mass-production of the alloys of the present invention and without being affected by Pb interfused as an unavoidable impurity in the case where the alloys of the present invention are produced using recycled materials, such as scraps or ingots comprising such scraps.

According to the invention of claim 6, it is made possible to provide a bronze-based alloy of low lead content, applicable to an alloy low in cooling velocity during the course of casting and making it possible to secure a tensile strength of at least 152 MPa at 180° C. in an alloy region having a secondary dendrite spacing of 14 μm or more.

According to the invention of claim 7, it is made possible to provide a bronze-based alloy of low lead content, which exhibits a high tensile strength even at high temperatures particularly for use as a material for a valve, water faucet clasp or water meter and which is therefore highly practicably valuable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 It is a graph showing the relationship between the content of P of the copper alloy of the present invention and the tensile strength thereof at 180° C.

FIG. 2 It is a schematic view of a dendrite.

FIG. 3 It is a micrograph showing the typical microstructure of CAC406.

FIG. 4 It is an explanatory view showing the measurement method for secondary dendrite arm spacing.

FIG. 5 It is a graph showing the relationship between the secondary dendrite spacing of alloys and the tensile strengths thereof at normal room temperature.

FIG. 6 It is a graph showing the relationship between the secondary dendrite spacing of alloys and the tensile strengths thereof at 180° C.

FIG. 7 It is a photograph showing the cut surface of a barrel part of a small valve (a general-purpose gate valve of leadless bronze having a nominal pressure of 10 K and a nominal diameter of ½).

FIG. 8 It is a photograph showing the cut surface of the barrel part in FIG. 7 that has been subjected to etching treatment with nitric acid.

FIG. 9 It is a graph showing the relationship between the content of Pb of the alloys and the tensile strength thereof at 180° C.

FIG. 10 It is a graph showing the relationship between the content of Ni of the copper alloy of the present invention and the tensile strength thereof at 180° C.

FIG. 11 It is a graph showing the relationship between the contents of Ni and P of the copper alloys of the present invention and the tensile strengths thereof at 180° C.

FIG. 12 It is a graph showing the influence of the Sb content on a leadless copper alloy.

FIG. 13 It is an explanatory view showing a casting method scheme for stepwise cast test pieces.

FIG. 14 It is an explanatory view showing the surface observed in the visible dye penetrant testing for each stepwise cast test piece.

FIG. 15 It is a conceptual diagram showing the P—Ni interaction.

FIG. 16 It is a SEM photograph showing the alloy of the present invention.

FIG. 17( a) is an SEM photograph showing the alloy of the present invention and (b) a photograph showing the texture of the fracture surface of the same alloy.

FIG. 18( a) is an SEM photograph showing the alloy in Comparative Example, and (b) a photograph showing the texture of the fracture surface of the same alloy.

FIG. 19 It is a diagram showing the microstructure of the alloy of the present invention.

FIG. 20 (a) to (g) are photographs each showing the distribution of the components of the alloy in FIG. 19 obtained by the EDX analysis.

FIG. 21 It is a graph showing the variation in tensile strength at high temperatures with respect to a conventional continuous cast product.

BEST MODE FOR CARRYING OUT THE INVENTION

The bronze-based alloy of low lead content according to the present invention is characterized in that a casting material has P contained therein to improve the tensile strength of the alloy at high temperatures. Particularly, the present invention is characterized in that within an alloy region having a secondary dendrite arm spacing interval of 14 μm or more in an ordinary leadless bronze alloy containing Bi, the tensile strength is improved at high temperatures exceeding 180° C. and specifically in that the tensile strength of 152 MPa at least at 180° C. can be ensured. The “bronze-based” alloy fundamentally comprises Sn, Zn, Bi, Cu and unavoidable impurities and, as preferable bronze-based alloys of low lead content, Cu—Sn—Zn—Bi-based alloys (hereinafter referred to as “Bi-based” alloys) and Sn—Zn—Se-based alloys (hereinafter referred to as “Bi—Se-based” alloys) can be cited.

The alloy of “low lead content” used in the present invention refers to an alloy having a Pb content lower than a bronze alloy containing Pb (CAC406 etc.) and not restricted to the content of Pb (0.25 mass % or less) as the residual component of a lead-free (leadless) copper alloy prescribed by JIS H5120 etc.

A “high-concentration P (phosphorus)” that will be used in the present invention refers to P in an amount exceeding 0.1 mass % that is larger than the amount of the residual P in the prior art.

The “P—Ni interaction” used in the present invention refers to a synergistic effect enabling the ratio of the effect by an increase in P content (enhancement in tensile strength) to be increased at high temperatures in the presence of Ni.

Here, the “tensile strength” used in the present invention refers to that evaluated with the Amsler tensile strength tester using the test piece No. 4 prescribed by JIS Z2201 that will be described later.

The “soundness of the casting” used in the present invention refers to the evaluation of the presence or absence of cast defects on the surface observed in the visible dye penetrant testing using a stepwise cast test piece that will be described later, made as acceptance if the evaluation is substantially the same as that for CAC406 or is capable of being judged as being in a state improvable by an amendment of a casting method scheme up to substantially the same as that for CAC 406.

The range of each component content and the reason for it will be described hereinafter.

P:0.1<P≦0.6 mass %

Generally, a copper alloy contains P in a relatively small amount of 0.01 mass % or more and 0.1 mass % or less. In order to promote the deoxidation of a molten metal and making the flowability of the molten metal good, for example, a casting produced by the sand casting contains residual P in an amount of 0.01 mass % or more and less than 0.1 mass %. For example, the content of P as the residual component in CAC406 is 0.05 mass % or less. Also as shown in Reports of the 146^(th) JFE Meeting, p. 30, the content of P, even when being positively added to a copper alloy for the purpose of preventing cast cracking, is 200 to 300 ppm (0.02 to 0.03 mass %). The P in these examples is added to the molten metal in a casting furnace or ladle, and the content of the residual P in a casting to be produced is 0.1 mass % or less.

As proposed in application No. PCT/JP2004/4757 cited above, the alloy has P contained therein in an amount of 0.01 to 0.5 mass %, preferably 0.05 to 0.1 mass % to improve the tensile strength at 100° C.

Incidentally, though less than 0.5 mass % of P is generally added with the aim of enhancing deoxidation of the molten metal to a molten metal in performing a method for continuously casting a copper alloy, the P is contained not positively in a cast product, and the content of P as the residual P is not disclosed.

On the other hand, the amount of P contained in the present invention contributes to the enhancement of the tensile strength at a high temperature (about 180° C.) and belongs to a high-concentration range of P to be positively contained, which range greatly surpasses the amount of P to be added for the purpose of deoxidizing molten metal and preventing cast cracking. The amount of the contained P exceeding 0.1 mass % can heighten the grain boundary strength while suppressing the production of Bi—Pb binary eutectic crystals, thereby contributing to the enhancement of the tensile strength at high temperatures.

In Example 1 to be described later (relationship between the content of P and the tensile strength at 180° C.), it is preferred that the upper limit of range in which P is contained and which satisfies the tensile strength of 152 MPa be 0.4 mass % and that the lower limit thereof be 0.2 mass %. Incidentally, the upper limit enables acquisition of the peak value of the tensile strength at 180° C. and, more preferably from the standpoint of const for commercial production, the upper limit is 0.4 mass %. Also as a value capable of securing the soundness of a casting in Example 5 to be described later and without requiring any change to a great extent in the casting method scheme during the commercial production, the upper limit is preferably 0.4 mass %.

Also, in the case further containing Ni to be described later, the interaction of the P and Ni enables the lower limit of the P content capable of infallibly acquiring the tensile strength of 152 MPa at 180° C. to be lowered. From this point of view, the lower limit of the P content is set to be preferably 0.12 mass % and more preferably 0.14 mass % and, as a result, it is made possible to acquire the tensile strength of 152 MPa at 180° C. at the upper limit suppressed to 0.33 mass %. Incidentally, it is effective to further suppress the P content when requiring better soundness of a casting and, in this case, the upper limit is preferably 0.2 mass %.

Ni: 0.0<Ni≦3.0 mass %

Generally, Ni in a copper alloy exhibits solubility into an a phase in the alloy to strengthen the matrix thereof, thereby contributing to the enhancement of mechanical properties of the alloy, the tensile strength thereof in chief. JP-A 2003-193157, for example, proposes a technique having 0.2 to 3.0 weight % of Ni contained in an alloy to secure the tensile strength at normal room temperature substantially the same as that of CAC406, in which a variation in tensile strength with an increase in Ni content assumes a gentle-mountain-shaped characteristic wherein the tensile strength reaches its peak when the Ni content falls in the range of 0.6 to 0.8 weight % in the exemplified alloy containing 0.01 to 0.02 weight % (130 to 200 ppm) of P (refer to FIG. 1 thereof).

In addition, as shown in Comparative Example that will be described later relative to Example 4 (relationship between the contents of P and Ni and the tensile strength at 180° C.), the leadless alloy containing P as the residual P (0.1 mass % or less) exhibits no discernible change in tensile strength at a high temperature (180° C.) with an increase in Ni content.

On the contrary, the content of Ni in the present invention contributes to the enhancement of the tensile strength at high temperatures on the premise of the content of P at a high concentration exceeding 0.1 mass % and, as shown in Example 4 that will be described later, this variation in tensile strength assumes a parabolic characteristic (with the axis as an x-axis) wherein the P—Ni interaction greatly enhances the tensile strength in the presence of a small amount of Ni content. Thus, even a small amount of Ni content makes it possible to suppress the P content to within a high-concentration range (0.1<P≦0.6 mass %) and enhance the tensile strength at high temperatures. This is extremely useful in due consideration of the fact that P is easy to evaporate from molten metal to make it difficult to control the P to a high concentration.

A concrete Ni content is only required to exceed 0 mass %. For example, 0.05 or 0.08 mass % of Ni is available. It is preferred to use 0.1 mass % of Ni, thereby enabling the tensile strength of 152 MPa at a high temperature (about 180° C.) while suppressing the P content.

On the other hand, since the excess amount of Ni content allows the enhancement of the tensile strength to be saturated, the upper limit of the Ni content is set to be 3.0 mass %. When judging from FIG. 10 (P=0.32 mass %) the state of saturation in the enhancement of the tensile strength at the preferable upper limit of P (0.4 mass %), it is better to adopt 2.0 mass % as the upper limit of the Ni content. As the upper limit of the range effectively enabling acquisition of the tensile strength even in a small amount of Ni content in view of cost reduction, 0.1 mass % may be adopted. Further in view of enabling the tensile strength of at least 152 MPa to be obtained at a high temperature (about 180° C.), it is better that the lower limit of the Ni content be 0.3 mass % and that the upper limit thereof be 0.6 mass %.

Bi: 0.1 to 3.0 mass %

This component is a substitute for Pb, has a low melting point and enters minute shrinkage cavities called microporosities produced in portions being finally solidified in the dendrite spacing of an alloy (casting) during the course of solidification of the casting, thereby enhancing the alloy soundness (resistance to pressure) and contributing to the ensuring of cuttability. While 0.1 mass % or more of Bi is effective for enhancing the cuttability, an alloy is required to contain 0.25 mass % of Bi in addition to the inclusion of Se in order to reduce the number of microporosities and secure its soundness. The excessive content of Bi, however, induces “inverse segregation” allowing the Bi to be concentrated together with Sn or high-concentration P on the surface of a casting during the course of the solidification of the casting and, in this case, there is a possibility of the number of microporisities in the casting being increased. Therefore, it is effective that the upper limit of Bi be set to be 3.0 mass % to secure the soundness of the alloy.

When it is required to effectively reduce the further number of microporosities, such as for the application requiring the resistance to pressure, it is effective that the lower limit of the Bi be 0.4 mass % and that the upper limit thereof be 2.5 mass %. Furthermore, in order to enable the mechanical machining under substantially the same cutting conditions as in the case of CAC406, the lower limit is preferably 1.0 mass %.

Incidentally, since an excessive content of Bi lowers the tensile strength, when necessitating infallible securement of the tensile strength at high temperatures at a level of commercial production, the upper limit of Bi is preferably 2.6 mass %. In addition, when making much of cost reduction in the commercial production, it is preferable to set the upper limit of Bi to be 2.0 mass %.

Zn: 3.0 to 10.0 mass %

This component is for enhancing hardness and other mechanical properties, particularly elongation, without imparting the influence of cuttability to an alloy. The content of Zr in an amount of 3.0 mass % or more promotes deoxidation of the molten metal effectively and enables the soundness of a casting and the flowability of the molten metal to be enhanced. Since Zr is comparatively inexpensive, though it is a component desirably contained in an amount as many as possible, the upper limit thereof is fixed at 10 mass % in view of possible deterioration of the casting environment by a vapor of Zn.

Then, when intending to infallibly acquire the deoxidation effect by Zn, the upper limit thereof is preferably 4.0 mass %. Furthermore, in the case of requiring the vapor pressure of Zn to be lowered taking particular note of the filling property of the molten metal in a casting mold, the upper limit thereof is preferably 9.0 mass %. Incidentally, in view of the fact that the optimum lower limit of Sn is 2.8 mass % described later, preferably the lower limit of a range of Sn not allowing the deposition of a 6 phase is 6.0 mass %.

Sn: 2.0 to 6.0 mass %

This component is for contributing to the enhancement of mechanical properties of an alloy, especially elongation and corrosion resistance, and the effective content thereof is 2.0 mass % or more. In consideration of the fact that Sn allows deposition of a hard and brittle δ phase and makes the machine workability and elongation lower and further of its cost, the upper limit thereof is fixed at 6.0 mass %.

When requiring substantially the same tensile strength as CAC406, the effective content of Sn is 2.8 mass % or more. Furthermore, in case where it is necessary to suppress the inverse segregation of solutes, such as P, Bi and Sn, even under different casting conditions during commercial production, the upper limit of Sn is preferably fixed at 5.5 mass %. Incidentally, in order to acquire a peak value of the tensile strength taking particular note of the tensile strength, the advantageous upper limit thereof is 4.5 mass %.

Se: 0.0<Se≦1.3

Se is a substitute for Pb and forms intermetallic compounds, such as Se—Zn and Cu—Se, in accordance with the ratio of contents of Cu and Zn, thereby securing the cuttability of the alloy while suppressing the content of Bi. The deposition of the intermetallic compounds causes the microporosities to be diffused, thereby enhancing the soundness of the alloy and stabilizing the tensile strength thereof. The excessive content of Se produces the deposition of brittle intermetallic compounds in a large amount to lower the tensile strength. The upper limit thereof is therefore fixed at 1.3 mass %.

Furthermore, when requiring the content of Se to be suppressed and substantially the same tensile strength as CAC406, it is better to fix the upper limit of Se at 0.35 mass %.

Pb: 0.005 to 2.0 mass %

It has heretofore been forced to use a material having the content of Pb eliminated to the utmost with the aim of controlling the content of Pb to 0.005 mass % or less to secure the tensile strength at a high temperature (180° C.). However, since the presence of P described later enables the tensile strength at high temperatures to be secured, it is expected to promote use of recycled materials containing Pb. Tb be specific, it is made possible to improve the tensile strength at high temperatures using Pb in the range of 0.005 to 2.0 mass % that falls within the region of low lead content in the present invention and to permit the content of Pb in an amount of 0.25 mass % corresponding to the standard of the Pb content in a leadless bronze valve stipulated in Japan, or less.

Unavoidable Impurities:

As the unavoidable impurities in the copper alloy of the present invention, besides the Pb, 0.3 mass % or less of Fe, 0.01 mass % or less of Al, 0.01 mass % or less of Si, 0.25 mass % or less of Mn, 0.3 mass % or less of S, 0.01 mass % or less of Mg, 0.01 mass % or less of Ti, 0.1 mass % of Zr, 0.3 mass % or less of Co, 0.3 mass % or less of Cr and 1.1 mass % or less of Sb can be cited.

In particular, the relationship between the content of Sb and the tensile strengths at normal room temperature and a high temperature was verified. Tables 2 and 3 below show the influence of the Sb content on leadless copper alloys each having chemical components and are plotted in FIG. 12. It has been confirmed from the figure that the Sb content has no discernible influence on the tensile strength and that no problem will arise if Sb exists as an unavoidable impurity.

TABLE 2 Chemical component value (mass %) Tensile strength at Cu Sn Zn Bi P Pb Sb room temperature (MPa) Balance 3.9 7.1 1.3 0.33 0.06 0.0 221 Balance 3.9 7.1 1.2 0.32 0.06 0.4 213 Balance 3.9 7.2 1.3 0.33 0.06 0.8 212 Balance 3.9 7.0 1.2 0.33 0.06 1.1 211

TABLE 3 Chemical component value (mass %) Tensile strength Cu Sn Zn Bi P Pb Sb at 180° C. (MPa) Balance 3.9 7.2 1.3 0.32 0.06 0.0 147 Balance 3.9 7.1 1.2 0.32 0.06 0.4 144 Balance 3.9 7.2 1.3 0.33 0.06 0.8 145 Balance 3.9 7.0 1.2 0.33 0.06 0.1 143

EXAMPLE 1

Preferred Examples of the alloys according to the present invention will be described in detail herein below. In Example 1, a target value of 152 MPa at a target temperature of 180° C. was determined as the reference value of tensile strength. Why 180° C. was adopted was that the maximum permissible working pressure in the case where a fluid was formed into saturated aqueous vapor in a bronze valve of 10 K nominal pressure or Class 150 was 1.0 MPa and that the saturated temperature corresponding to the working pressure was 180° C. Why 152 MPa was adopted was compliant with the fundamental idea that the target tensile strength value of a material main body in the “pressure container structure” prescribed under JIS B 8270 was four times the basic allowable pressure in consideration of the safety etc. of products using this material and therefore that a value four times the basic allowable stress of CAC406 at 200° C. that was 38 MPa was used. As a result, the 152 MPa at 180° C. was proved to be suitable for use of a pressure container for valves to which the alloy of the present invention was applicable.

First, in the present test, the relationship between the content of P and the tensile strength at 180° C. was verified. The compositions of each sample are shown in Table 4. The results of the test are shown in Table 4 and plotted in FIG. 1. Incidentally, the samples in Example 1 were taken from sand castings. Test samples in the tensile test were cast in accordance with JIS-A method scheme at a pour point of 1130° C. using a casting mold of Co₂ and then subjected to cutting work to fabricate the test piece No. 4 prescribed under JIS Z2201. The test pieces were tested using an Amsler tensile strength tester. The conditions of this tensile test were adopted in other Examples taking samples from sand castings.

TABLE 4 Tensile Chemical component value (mass %) strength at No. Cu Sn Zn Bi Se Pb P Ni 180° C. (MPa) Comp. 1-1 Balance 4.3 8.0 1.3 0.2 0.05 0.02 0.0 80 Example 2 Balance 4.3 7.9 1.4 0.2 0.05 0.10 0.0 110 Present 3 Balance 4.1 8.1 1.4 0.2 0.05 0.18 0.0 125 Invention 4 Balance 4.3 8.0 1.4 0.2 0.05 0.26 0.0 152 5 Balance 4.3 8.0 1.4 0.2 0.05 0.34 0.0 165 6 Balance 4.1 8.2 1.4 0.2 0.05 0.50 0.0 152 Com. 7 Balance 4.1 8.1 1.4 0.2 0.05 0.74 0.0 134 Example 8 Balance 4.1 8.1 1.4 0.2 0.06 0.98 0.0 95

(APPENDIX TABLE 4) Tensile strength Sample Chemical component value (mass %) at 180° C. Classification No. Cu Sn Zn Bi Se Pb P Ni (MPa) Present Bi—Se- 1-9 Bal. 3.3 4.1 1.5 0.5 0.05 0.37 0.0 184 Invention based 10 Bal. 3.1 4.0 2.1 0.4 0.06 0.22 0.0 158 allot 11 Bal. 5.4 4.1 2.2 0.5 0.07 0.37 0.0 176 12 Bal. 3.1 8.3 1.3 0.2 0.06 0.35 0.0 164 13 Bal. 3.2 8.1 1.4 0.4 0.05 0.22 0.0 153 14 Bal. 3.7 8.1 2.1 0.4 0.06 0.37 0.0 167 15 Bal. 5.9 8.1 1.5 0.4 0.06 0.37 0.0 178 16 Bal. 5.9 8.0 2.1 0.4 0.06 0.24 0.0 158 Bi- 17 Bal. 3.2 4.0 1.4 0.0 0.05 0.22 0.0 168 based 18 Bal. 3.2 4.1 2.1 0.0 0.06 0.36 0.0 194 alloy 19 Bal. 5.5 4.0 1.5 0.0 0.06 0.37 0.0 185 20 Bal. 5.5 4.0 2.2 0.0 0.06 0.24 0.0 156 21 Bal. 3.0 8.4 1.1 0.0 0.05 0.32 0.0 182 22 Bal. 3.2 8.2 1.4 0.0 0.06 0.36 0.0 176 23 Bal. 3.6 8.0 2.0 0.0 0.06 0.23 0.0 153 24 Bal. 5.8 8.1 2.1 0.0 0.61 0.37 0.0 167

Sample Nos. 1-1 to 8 have the content of P, which is one of the characteristic components of the copper alloy of the present invention, varied in the Bi—Se-based alloys. It is found from the test results that the alloys containing P of a high concentration exceeding 0.10 mass % have been improved in tensile strength at a high temperature of 180° C. It is further found from the graph of FIG. 1 that in order to achieve the target value of 152 MPa in Example 1, P has to be contained in the range of 0.26 to 0.50 mass %.

Sample Nos. 1-9 to 16 shown in Appendix Table 4 contain high-concentration P, which is one of the characteristic components of the copper alloy of the present invention, with the contents of Sn, Ze, B and Se, which are principal components in the Bi—Se-based alloys similar to sample Nos. 1-1 to 8, varied. In addition, Sample Nos. 1-17 to 24 contain high-concentration P, which is one of the characteristic components of the copper alloy of the present invention, with the contents of Sn, Zn and Bi, which are principal components in the copper alloy (Bi-based alloy) of the present invention, varied.

The tensile strengths of these samples at 180° C. were verified. When considering Appendix Table 4, it is found from the test results that the target value of 152 MPa at a high temperature (180° C.) has been achieved in Examples having the following component ranges by dint of the presence of high-concentration P.

<Bi—Se-based Alloy>

The compositions thereof consist of 3.0 to 6.0 (preferably 3.1 to 5.9) mass % of Sn, 4.0 to 9.0 (preferably 8.3) mass % of Zn, 1.0 to 3.0 (preferably 1.3 to 2.2) mass % of Bi, 0.2 to 0.5 mass % of Se, 0.20 (preferably 0.22) to 0.50 mass % of P and the balance of Cu and unavoidable impurities.

<Bi-Based Alloy>

The compositions thereof consist of 3.0 to 6.0 (preferably 5.8) mass % of Sn, 4.0 to 9.0 (preferably 8.4) mass % of Zn, 1.0 to 3.0 (preferably 1.1 to 2.2) mass % of Bi, 0.20 to 0.40 (preferably 0.22 to 0.27) mass % of P and the balance of Cu and unavoidable impurities.

EXAMPLE 2

Next, the tensile strengths of bronze-based copper alloys of low lead content at high temperatures are quantitatively grasped to show the ranges of the components of the alloys in compliance with the present invention and verify the effects of the present invention.

It is generally known that the tensile strength of an alloy has relationship with the size of the microstructure thereof. In view of this, the present test used the secondary dendrite arm spacing as a criterion showing the size of the microstructure of an alloy. Here, the term “dendrite” means one of the crystal-growth modes in the metallic solidification. FIG. 2 is a schematic view showing the dendrite, in which when the stem is defined as a primary dendrite arm (primary branch) and the branches produced from the primary branch as secondary dendrite arms (secondary branches). It has been known that the dendrite arm spacing has a great influence on the mechanical properties etc. of a casting. FIG. 3 is a micrograph showing the typical microstructure of CAC406, from which it can be observed that the secondary dendrite arms have been well developed and well aligned.

Therefore, the secondary dendrite arms were measured using the measurement method for secondary dendrite arm spacing to evaluate the size of the microstructure. The measurement method for secondary dendrite arm spacing is a method for measuring the average spacing in the well-aligned dendrite arms as shown in FIG. 4( a). To be specific, a search is made, from the microstructure, for dendrite arms grown as aligned in parallel, then a line of optional length substantially orthogonal to the dendrite arms is drawn, and the length L of the line intersecting the dendrite arms is divided by the number (n−1) of the dendrite arms to obtain a quotient ds. That is to say, the size of the secondary dendrite arms is expressed as L/(n−1). Incidentally, the microstructures of a test piece casting differ in size from one locality to be observed to another and, since the test piece casting has a polycrystalline structure, the individual crystal grains show different ways to grow the dendrite arms. In the present test, the methods for measuring the secondary dendrite arm spacing of the test pieces are unified as described below. Furthermore, when failing to observe clear crystal grain boundaries in the actually cast product, item 3 below is applied.

1. Localities to be Observed:

JIS No. 4 tensile test pieces, gauge mark parts and axial transverse sections.

2. Localities to be Measured:

The localities in which the secondary dendrite arms are aligned in the individual crystal grains near the center of the axial transverse section of a test piece as shown in FIG. 4( b) are specified, and three or more crystal grains in total are measured.

3. Number of Dendrites Measured:

30 dendrites each having five or more dendrite arms aligned.

FIG. (4 c) illustrates an example of the measurement of CAC306. Since the average value of the secondary dendrite arm spacing is converged when the number of the dendrites exceeds 10, the influence caused by the difference in locality to be measured can be eliminated.

In the tests based on the above method, the tensile strengths of castings at normal room temperature and at a high temperature, which casting were divided into sand castings, metal mold castings and continuously cast castings, were verified. The compositions of samples are shown in Table 5 (normal room temperature) and Table 6 (high temperature). The test results are shown in these tables and plotted in FIG. 5 (normal room temperature) and FIG. 6 (high temperature). Incidentally, the normal room temperature used in this Example is about 23° C. and this is applicable to other Examples.

TABLE 5 Sample Secondary Tensile Details of Chemical component value (mass %) dendrite arm strength Classification No. specifications Cu Sn Zn Bi Se Pb P Ni spacing (μm) (MPa) Comp. Leadless 2-1 Continuously Bal. 4.5 7.0 2.6 0.0 0.05 0.10 0.0 10.8 303 Example copper cast casting φ25 alloy 2 Continuously Bal. 4.5 7.1 2.5 0.0 0.05 0.09 0.0 11.2 289 cast casting φ30 3 Continuously Bal. 4.5 7.0 2.5 0.0 0.05 0.09 0.0 13.0 280 cast casting φ35 4 Continuously Bal. 4.6 7.1 2.6 0.0 0.05 0.07 0.0 14.2 272 cast casting φ42 5 Metal mold Bal. 4.0 8.0 1.3 0.2 0.04 0.02 0.0 20.6 288 casting 6 Sand casting 1 Bal. 5.0 6.9 2.6 0.0 0.05 0.02 0.0 45.0 218 7 Sand casting 2 Bal. 4.4 8.0 1.3 0.2 0.04 0.02 0.0 46.0 221 Lead- 2-8 Continuously Bal. 4.1 5.6 0.0 0.0 5.00 0.52 0.0 8.8 287 containing cast casting φ25 copper alloy 9 Continuously Bal. 4.3 5.4 0.0 0.0 4.80 0.74 0.0 13.7 267 (CAC406) cast casting φ42 10  Metal mold Bal. 4.0 5.7 0.0 0.0 4.90 0.24 0.0 17.5 288 casting 11  Sand casting Bal. 4.0 5.7 0.0 0.0 4.90 0.24 0.0 46.8 237 Present Bi—Se-based  2-12 Metal mold Bal. 3.9 8.1 1.3 0.0 0.06 0.37 0.0 15.5 320 Invention alloy casting 13  Sand casting Bal. 4.2 7.7 1.3 0.2 0.06 0.34 0.0 42.9 218 Bi-based 14  Sand casting Bal. 2.3 9.3 1.3 0.2 0.05 0.32 0.9 48.8 205 alloy 15  Sand casting Bal. 2.0 6.5 2.6 0.0 0.06 0.33 0.9 38.0 256

TABLE 6 Sample Secondary Tensile Details of Chemical component value (mass %) dendrite arm strength Classification No. specifications Cu Sn Zn Bi Se Pb P Ni spacing (μm) (MPa) Comp. Leadless 2-21 Continuously Bal. 4.5 7.0 2.6 0.0 0.05 0.10 0.0 10.8 257 Example copper cast casting φ25 alloy 22 Continuously Bal. 4.5 7.1 2.5 0.0 0.05 0.09 0.0 11.2 224 cast casting φ30 23 Continuously Bal. 4.5 7.0 2.5 0.0 0.05 0.09 0.0 13.0 236 cast casting φ35 24 Continuously Bal. 4.6 7.1 2.6 0.0 0.05 0.07 0.0 14.2 155 cast casting φ42 25 Metal mold Bal. 4.0 8.0 1.3 0.2 0.04 0.02 0.0 20.6 107 casting 26 Sand casting 1 Bal. 5.0 7.1 2.3 0.0 0.05 0.02 0.0 45.0  79 27 Sand casting 2 Bal. 4.4 8.0 1.4 0.2 0.04 0.02 0.0 46.0  85 Lead- 2-28 Continuously Bal. 4.1 5.6 0.0 0.0 5.00 0.05 0.0 8.8 260 containing cast casting φ25 copper alloy 29 Continuously Bal. 4.3 5.4 0.0 0.0 4.80 0.07 0.0 13.7 237 (CAC406) cast casting φ42 30 Metal mold Bal. 4.0 5.7 0.0 0.0 4.90 0.02 0.0 17.5 268 casting 31 Sand casting Bal. 4.0 5.7 0.0 0.0 4.90 0.02 0.0 46.8 200 Present Bi—Se-based 2-32 Metal mold Bal. 3.6 8.0 1.3 0.2 0.05 0.36 0.0 15.9 255 Invention alloy casting 33 Sand casting Bal. 3.8 7.8 1.4 0.2 0.06 0.36 0.0 42.9 190 34 Sand casting Bal. 4.8 6.9 1.6 0.5 0.06 0.15 1.0 51.4 — Bi-based 2-35 Sand casting Bal. 6.0 7.2 2.5 0.0 0.06 0.17 0.0 49.4 — alloy 36 Sand casting Bal. 2.3 9.3 1.3 0.0 0.05 0.32 0.9 48.8 171 37 Sand casting Bal. 2.9 6.5 2.6 0.0 0.06 0.33 0.9 38.0 220

It is found from the test results that the smaller the secondary dendrite arm spacing, the smaller the degree of decrease in tensile strength at 180° C. In the meantime, though it has conventionally been common knowledge that the tensile strength of a continuously cast casting is not lowered, as is clear from the test results, it has been confirmed that the tensile strength of the continuously cast casting is lowered depending on the diameter thereof. In particular, the castings having a large diameter lowered their tensile strengths. It is conceivable that the reason for it is that a casting of a larger diameter causes the cooling rate thereof to be delayed to make the secondary dendrite arm spacing larger.

Here, the “continuously cast casting” is molded by means of “continuous casting” that continuously extracts solidified castings from below while pouring molten metal from above into a hollow and vertical metal mold, for example. The solidification of molten metal is promoted with cooling equipment, such as water-cooling.

On the contrary, the “sand casting” is molded by means of “sand casting” that pours molten metal into a casting mold formed of solidified casting sand, leaves the molten metal standing to cool it with air and takes solidified metal part out of the casting mold, and the “metal mold casting” is molded by means of “metal mold casting” that pours molten metal into a casting mold formed of metal, leaves the molten metal standing to cool it with air and takes solidified metal part out of the casting mold. Though the cooling rates of castings differs depending on the difference of the methods of casting, size of castings and scheme of casting methods, since the “sand casting” and “metal mold casting” used in the present example adopted slower cooling rates than the “continuously cast casting,” the secondary dendrite arm spacing was further widened to possibly lower the tensile strength.

On the other hand, it is found that the copper alloys of the present invention are improved in tensile strength at high temperatures so as not to be lowered without being affected by the secondary dendrite arm spacing. That is to say, the copper alloys of the present invention are those improved in tensile strength at high temperatures without being affected by the difference in method of casting (cooling rate). In other words, it is found that these alloys are those improved in tensile strength at high temperatures while permitting the manufacture thereof even through the use of the conventional method of casting (cooling rate). In addition, since the copper alloys of the present invention exhibits a tendency similar to that of CAC406 as shown in FIGS. 5 and 6, they can secure the tensile strength up to high temperatures as a substitute for CAC406.

Incidentally, since the secondary dendrite arm spacing at the target value of 152 MPa during the course of the transit in tensile strength of leadless copper alloy at a high temperature (180° C.) is around 14 μm, as shown in FIG. 6, this spacing of 14 μm has been determined as a boundary reference value in the alloy region suitable for the copper alloys of the present invention. According to the copper alloys of the present invention, therefore, it is made possible to secure the tensile strength of at least 152 MPa at 180° C. within the alloy region exhibiting a secondary dendrite arm spacing of 14 μm or more.

Here, the actual products are tested for the secondary dendrite arm spacing. Particularly, adopted were small-sized valves (pressure resistance: 10 K, nominal diameter: ½, general-purpose gate valves of leadless bronze, sand castings). FIG. 7 is the cut surface of a barrel part, and FIG. 8 shows the same cut surface after being subjected to etching treatment with nitric acid. Sections (alloy regions) 1, 2 and 3 of different-thickness walls have secondary dendrite arm spacing of 27.9 μm, 24.7 μm and 23.4 μm, respectively. Since any of these has an arm spacing exceeding 14 μm, ordinary sand cast products can be judged as objects to be improved. Incidentally, a section having an arm spacing of 14 μm or more may be part (alloy region) of a casting and, in this case, the whole of a casting part constitutes an object to which the copper alloy of the present invention is applied.

The method of measurement comprises, as shown in FIG. 8, etching treatment, use of an electron microscope in a state wherein an understanding of the metal texture is made easy to measure the secondary dendrite arm spacing. Thus, even in one casting, the difference in thickness induces a difference in secondary dendrite arm spacing and, therefore, it is made possible to quantitatively grasp the tensile strength of local alloy regions and make acceptance/rejection criteria of products resulting from the tensile strength.

EXAMPLE 3

Next, the relationship between the Pb content and the tensile strength at 180° C. was verified with respect to the copper alloys of the present invention (Bi—Se-based alloys). The composition of each sample is shown in Table 7 and plotted in FIG. 9. Incidentally, each sample was collected from a sand casting.

TABLE 7 Tensile Chemical composition value (mass %) strength No. Cu Sn Zn Bi Se Pb P Ni (MPa) Compar- 3-1 Bal. 3.9 8.1 1.3 0.2 0.003 0.02 0.0 204 ative  2 Bal. 4.0 8.5 1.3 0.2 0.004 0.02 0.0 212 Example  3 Bal. 4.1 8.5 1.3 0.2 0.005 0.02 0.0 174 (leadless  4 Bal. 4.1 8.6 1.3 0.2 0.008 0.02 0.0 118 copper  5 Bal. 4.0 8.5 1.3 0.2 0.01 0.02 0.0 105 alloy  6 Bal. 4.0 8.2 1.3 0.2 0.02 0.02 0.0 109  7 Bal. 4.0 8.2 1.3 0.2 0.03 0.02 0.0 97  8 Bal. 4.1 8.1 1.3 0.2 0.04 0.02 0.0 94  9 Bal. 3.9 8.1 1.3 0.2 0.05 0.02 0.0 91 10 Bal. 4.0 8.1 1.3 0.2 0.20 0.02 0.0 86 Present 3-11 Bal. 4.1 8.2 1.4 0.2 0.00 0.36 0.0 232 Invention 12 Bal. 4.1 8.1 1.4 0.2 0.01 0.36 0.0 196 (Bi—Se- 13 Bal. 4.1 8.2 1.4 0.2 0.05 0.36 0.0 174 based 14 Bal. 3.9 8.2 1.4 0.2 0.10 0.35 0.0 166 alloy 15 Bal. 3.8 8.0 1.4 0.2 0.30 0.35 0.0 167 16 Bal. 3.9 8.1 1.4 0.2 0.50 0.35 0.0 157 17 Bal. 3.9 8.1 1.4 0.2 0.70 0.36 0.0 152 18 Bal. 3.9 8.1 1.5 0.2 1.10 0.36 0.0 159 19 Bal. 3.9 8.1 1.4 0.2 1.30 0.36 0.0 154 20 Bal. 4.1 8.1 1.4 0.2 2.00 0.36 0.0 153

It is found from the present test results that in the copper alloys of the present invention containing a high concentration of P, while an increase in Pb content allows a gradual decrease in tensile strength, no discernible decrease in tensile strength is found when the Pb content exceeds 0.5 mass % and that the target value of 152 MPa at 180° C. can substantially be secured. On the other hand, in leadless copper alloys shown as Comparative Examples, the tensile strength is conspicuously decreased and, when the Pb content exceeds 0.005 mass %, the target value of 152 MPa at 180° C. cannot be satisfied. Thus, the alloys of the present invention makes it possible to secure high tensile strengths at high temperatures even in the presence of Pb and, therefore, are useful as recycled materials.

EXAMPLE 4

Next, the relationship between the Ni content and the tensile strength at 180° C. was verified with respect to the copper alloys of the present invention (Bi-based alloys). The composition of each sample is as shown in Table 8 and the test results are shown in the same table and plotted in FIG. 10. Incidentally, each sample in Example 4 was obtained from a sand casting.

TABLE 8 Tensile strength at Tensile strength Chemical composition value (mass %) normal room at 180° C. No. Cu Sn Zn Bi Se Pb P Ni temperature (MPa) (MPa) 4-1 Bal. 3.6 7.1 1.2 0.0 0.5 0.32 0.0 217 151 2 Bal. 3.7 7.1 1.2 0.0 0.5 0.32 0.1 233 161 3 Bal. 3.6 7.1 1.2 0.0 0.5 0.32 0.2 226 169 4 Bal. 3.6 7.1 1.3 0.0 0.5 0.32 0.4 250 191 5 Bal. 3.6 7.0 1.2 0.0 0.5 0.32 0.6 267 194 6 Bal. 3.6 7.0 1.2 0.0 0.5 0.32 0.8 265 213 7 Bal. 3.6 7.0 1.2 0.0 0.5 0.31 1.0 287 206 8 Bal. 3.6 7.0 1.2 0.0 0.5 0.32 1.2 276 208 9 Bal. 3.6 6.8 1.2 0.0 0.5 0.32 1.9 303 239 10  Bal. 3.6 6.8 1.2 0.0 0.5 0.32 3.0 306 220

APPENDIX TABLE 8 Tensile strength Chemical (MPa) composition Normal Sample value (mass %) room Classification No. Cu Sn Zn Bi Se Pb P Ni temperature 180° C. Present Bi- 4-11 Bal. 5.7 9.4 0.1 0.0 0.01 0.18 0.4 271 250 Invention based 12 Bal. 2.7 8.5 0.3 0.0 0.01 0.19 0.4 263 221 alloy 13 Bal. 2.9 6.5 2.6 0.0 0.06 0.33 0.9 256 220 14 Bal. 2.8 9.5 0.5 0.0 0.01 0.17 0.4 258 234 15 Bal. 2.3 9.4 1.3 0.0 0.05 0.32 1.0 205 171 16 Bal. 3.2 7.4 1.4 0.0 0.01 0.12 0.4 — 191 Bi—Se- 17 Bal. 4.7 4.8 2.9 0.1 0.01 0.16 0.3 251 210 based 18 Bal. 4.7 4.9 2.5 1.3 0.01 0.18 0.4 240 216 alloy Comparative 19 Bal. 7.2 11.2 2.9 1.1 0.06 0.60 3.0 178 146 Example 20 Bal. 7.1 11.5 3.0 1.2 0.06 0.35 1.0 178 140

It was found from the present test results that addition of Ni to the copper alloy of the present invention containing P in a high concentration enhanced the tensile strength both at normal room temperature and at high temperatures. It can be confirmed particularly from FIG. 10 that when the Ni content is in the range of 0.1 to 3.0 mass %, the target value of 152 MPa is secured.

Next, the tensile strengths at normal room temperature and at 180° C. were verified with respect to each of the following samples. Indicated by Nos. 4-11 to 16 are samples of the copper alloys of the present invention (Bi-based alloys), with the contents of the principal components of Sn, Zn and Bi varied and with the contents of the characterizing components of P and Ni varied. In addition, indicated by Nos. 4-17 and 18 are samples of the copper alloys of the present invention (Bi—Se-based alloys), with the contents of the principal components of Bi and Se varied, and by Nos. 4-19 and 20 are samples of Comparative Examples, with the content of the principal component Zn increased.

Furthermore, here, the tensile strengths at 180° C. were verified with respect to the copper alloys of the present invention (Bi-based alloys) containing 0.14 mass %, 0.22 mass %, 0.28 mass % and 0.32 mass %, respectively, of P having added thereto 0, 0.20 mass %, 0.40 mass % and 0.60 mass %, respectively, of Ni. As Comparative Examples, those of the alloys containing 0.02 mass % and 0.10 mass %, respectively of P were measured. The composition of each sample is shown in Table 9 and the test results are shown in the same table and plotted in FIG. 11.

TABLE 9 Chemical composition value (mass %) Tensile strength No. Cu Sn Zn Bi Se Pb P Ni at 180° C. (MPa) Comp. 4-21 Bal. 3.7 6.8 1.2 0.0 0.05 0.09 0.00 100 Ex. 22 Bal. 3.9 6.8 1.2 0.0 0.04 0.10 0.16 108 23 Bal. 3.8 6.7 1.2 0.0 0.04 0.10 0.42 110 24 Bal. 3.9 6.8 1.2 0.0 0.04 0.10 0.59 112 Present 25 Bal. 3.9 6.9 1.3 0.0 0.06 0.14 0.00 117 Invention 26 Bal. 3.8 7.0 1.3 0.0 0.06 0.14 0.16 144 27 Bal. 3.9 7.0 1.3 0.0 0.06 0.15 0.43 163 28 Bal. 3.8 6.9 1.3 0.0 0.06 0.15 0.60 161 29 Bal. 3.9 7.1 1.3 0.0 0.06 0.21 0.01 137 30 Bal. 3.9 7.1 1.2 0.0 0.05 0.22 0.17 157 31 Bal. 3.9 7.1 1.3 0.0 0.06 0.22 0.40 181 32 Bal. 3.8 7.1 1.3 0.0 0.06 0.22 0.60 176 33 Bal. 3.8 7.1 1.3 0.0 0.06 0.28 0.01 142 34 Bal. 3.8 7.2 1.3 0.0 0.06 0.28 0.17 180 35 Bal. 4.0 7.1 1.3 0.0 0.06 0.28 0.42 183 36 Bal. 3.9 7.1 1.3 0.0 0.06 0.27 0.61 210 37 Bal. 3.9 7.2 1.3 0.0 0.06 0.32 0.01 147 38 Bal. 3.9 7.0 1.3 0.0 0.06 0.33 0.16 190 39 Bal. 3.9 7.1 1.2 0.0 0.06 0.32 0.40 200 40 Bal. 4.0 7.1 1.3 0.0 0.06 0.33 0.60 213 Comp. 41 Bal. 3.5 7.0 1.2 0.0 0.05 0.02 0.00 87 Ex. 42 Bal. 3.5 7.0 1.2 0.0 0.05 0.02 0.39 79

It was confirmed from the present test results that in respect of the tensile strengths at high temperatures the higher the concentration of the P content, the larger the feature-enhancing effect of the Ni content was and therefore that there was an interaction of P and Ni. To be specific, in Comparative Examples having a P content of low concentration, the enhancement in tensile strength even in the presence of Ni was small, whereas the samples containing P in a concentration exceeding 0.10 mass % were greatly enhanced in tensile strength in the presence of an Ni content. Particularly, in the samples containing P in a concentration exceeding 0.16 mass %, the addition of the Ni content particularly in the range of 0.16 to 0.61 mass % in accordance with the characteristics shown in Table 9 and FIG. 11 to the samples enabled the target value of 152 MPa in tensile strength to be obtained.

Considering Table 8, Appendix Table 8 (Bi-based alloys) and Table 9, it is found from the test results that Examples having the following composition range can achieve the target value of 152 MPa in tensile strength at a high temperature (180° C.) in consequence of having contained a high concentration of P therein.

<Bi-Based Alloy>

The compositions thereof consist of 2.0 to 6.0 (preferably 2.3 to 5.7) mass % of Sn, 6.0 to 10.0 (preferably 6.5 to 9.5) mass % of Zn, 0.1 to 3.0 (preferably 2.6) mass % of Bi, 0.12 to 0.40 (preferably 0.33) mass % of P, 0.1 to 3.0 mass % of Ni and the balance of Cu and unavoidable impurities.

Incidentally, Bi—Se-based alloys containing 0.1 to 1.3 mass % of Se in addition to the components of the Bi-based alloy can be applied to the present invention.

FIG. 15 is a conceptual diagram showing the P-Ni interaction. As compared with the alloy of Comparative Example containing P of low concentration (0.1≦P), the copper alloy of the present invention containing P of high concentration (0.1<P≦0.6) is enhanced in tensile strength at high temperatures (refer to A in FIG. 15). On the contrary, when containing Ni in addition to P, the alloy of Comparative Example containing P of low concentration exhibits a slight increase in tensile strength at high temperatures (refer to C in FIG. 15), whereas the copper alloy of the present invention containing P of high concentration exhibits a large increase in tensile strength at high temperatures to the neighborhood of the tensile strength at normal room temperature (refer to B in FIG. 15). Thus, the P—Ni interaction implies a synergistic effect (refer to B and C in FIG. 15) of increasing an enhancing ratio of the effect with an increase in P content (tensile strength) at high temperatures owing to the presence of Ni.

EXAMPLE 5

Next, the copper alloys of the present invention were tested for casting soundness and the test results will be described. FIG. 13 is an explanatory view showing the casting method scheme for stepwise cast test pieces, and FIG. 14 an explanatory view showing the location of each test piece measured.

By the casting method scheme for the stepwise casting test pieces shown in FIG. 13, samples numbered 5-1 to 17 were cast. Each of the castings obtained was cut to obtain a test piece shown in FIG. 14. The cut surface of each test piece was polished and then subjected to the visible dye penetrant testing. The “visible dye penetrant testing” comprises the steps of spraying a penetrant onto the cut surface of a test piece, leaving the penetrant standing for 10 minutes, then wiping away the penetrant, further spraying a developer onto the cut surface having the penetrant wiped away to determine the presence or absence of casting defects from red marks having emerged on the cut surface. The casting method scheme for the stepwise test piece comprises the step of pouring molten metal from the side of the stepwise part having a wall thickness of 40 mm via a gate riser measuring 70 mm in diameter×160 mm in length starting with a pouring gate having a diameter of 25 mm. The casting conditions include performing resolution in an experimental high-frequency furnace, using a meltage of 12 kg, adopting a pour point of 1180° C. and using a Co₂ casting mold.

Indicated by Nos. 5-1 to 7 shown in Table 10 are samples of the copper alloys of the present invention (Bi-based alloys), with the contents of the principal components of Sn and Zn varied and the content of the characterizing component of P in the present invention varied.

Then, Indicated by Nos. 5-8 to 17 are samples of the copper alloys of the present invention (Bi-based alloys), with the contents of the principal components of Sn, Zn and Bi varied and the contents of the characterizing components of P and Ni varied. In addition, indicated by Nos. 5-18 to 20 are samples of the copper alloys of the present invention (Bi—Se-based alloys), with the contents of the principal components of Sn, Zn and Bi varied and the contents of the characterizing components of P and Ni in the present invention varied.

Furthermore, when considering Table 10, the samples containing about 0.36 mass % of P (Nos. 5-1 to 3, 19 and 19) are confirmed to have slight defects with respect to their stepwise casting test pieces, but are the samples improvable in consequence of correcting the casting method scheme in manufacturing products to be mass-produced, such as valves etc.

Moreover, with respect to the samples containing Ni, the samples containing P in a high concentration of 0.31 mass % (Nos. 5-8 and 9) were confirmed to have no defect and obtain good castings. It is found from the present test results that in the examples having the following ranges of components, it is made possible to achieve the target value of tensile strength that is 152 MPa at a high temperature (180° C.) owing to the presence of a high concentration of P and as well secure the casting soundness.

<Bi-based Alloys>

The compositions thereof consist of 2.5 (preferably 2.9) to 6.0 mass % of Sn, 4.0 (preferably 3.9) to 8.0 mass % of Zn, 0.5 to 3.0 (preferably 2.5 mass % of Bi, 0.15 to 0.40 (preferably 0.36) mass % of P, 0<Ni≦2.0 (preferably 1.9) and the balance of Cu and unavoidable impurities.

Incidentally, with respect to the Bi—Se-based alloys, those containing Se in the range of 0.1 to 1.3 in addition to the components of each of the Bi-based alloys are available.

TABLE 10 Acceptance: ◯ Visible dye Sample Chemical component value (mass %) penetrant Classification No. Cu Sn Zn Bi Se Pb P Ni testing Present Bi- 5-1 Bal. 4.3 8.0 1.4 0.0 0.05 0.36 0.0 ◯ Invention Based 2 Bal. 3.3 6.0 1.4 0.0 0.05 0.36 0.0 ◯ alloy 3 Bal. 4.4 3.9 1.4 0.0 0.05 0.37 0.0 ◯ 4 Bal. 3.0 7.5 1.3 0.0 0.04 0.18 0.0 ◯ 5 Bal. 3.0 7.0 1.3 0.0 0.05 0.18 0.0 ◯ 6 Bal. 3.1 5.8 1.3 0.0 0.05 0.18 0.0 ◯ 7 Bal. 2.9 4.8 1.3 0.0 0.04 0.17 0.0 ◯ 8 Bal. 3.0 7.8 1.3 0.0 0.09 0.31 0.4 ◯ 9 Bal. 3.0 7.8 1.3 0.0 0.11 0.31 0.8 ◯ 10 Bal. 3.0 7.9 1.2 0.0 0.08 0.19 0.4 ◯ 11 Bal. 3.0 7.9 1.2 0.0 0.10 0.17 0.8 ◯ 12 Bal. 3.1 7.6 1.3 0.0 0.05 0.18 0.5 ◯ 13 Bal. 3.1 6.8 1.3 0.0 0.05 0.18 0.5 ◯ 14 Bal. 3.0 6.3 1.3 0.0 0.05 0.17 0.5 ◯ 15 Bal. 3.1 4.9 1.3 0.0 0.07 0.18 0.5 ◯ 16 Bal. 5.5 6.8 0.5 0.0 0.05 0.15 1.9 ◯ 17 Bal. 6.0 7.0 2.5 0.0 0.06 0.16 1.9 ◯ Bi—Se- 18 Bal. 4.3 7.9 1.4 0.2 0.06 0.36 0.0 ◯ based 19 Bal. 4.3 4.0 1.4 0.2 0.05 0.36 0.0 ◯ alloy 20 Bal. 4.8 6.9 1.6 0.5 0.06 0.15 1.9 ◯

EXAMPLE 6 (Cuttability Test)

The pieces subjected to cuttability test were evaluated by machining, with a lathe, cylindrical substances to be machined and using a cuttablity index in the cutting resistance exerted on a turning tool when the cutting resistance of a bronze casing CAC406 was regarded as 100. The test conditions include using the pour point of 1160° C. (in the Co₂ casting mold), the shape of the substance to be cut measuring 31 mm in diameter and 300 mm in length, 3.2 as the surface coarseness R_(A), 3.0 mm as the cut depth, 1800 rpm as the number of revolutions of the lathe, 0.2 mm/rev as the feeding amount and no oil.

The results of the cuttability test are shown in Table 11.

TABLE 11 Index Sample Chemical composition value (mass %) (cutting Classification No. Cu Sn Zn Bi Se Pb P  Ni by 3 mm) Present Bi- 6-1 Bal. 3.7 6.9 1.0 0.0 0.05 0.32 0.0 80 Invention based 2 Bal. 3.9 7.0 1.5 0.0 0.06 0.33 0.0 83 alloy 3 Bal. 2.9 6.7 1.3 0.0 0.00 0.17 0.4 83 4 Bal. 2.9 6.6 1.4 0.0 0.00 0.34 0.8 83 Bi—Se- 5 Bal. 3.9 6.9 1.0 0.1 0.06 0.33 0.0 84 based 6 Bal. 3.9 7.1 1.0 0.2 0.06 0.33 0.0 81 alloy 7 Bal. 3.9 7.1 1.5 0.1 0.06 0.33 0.0 87 8 Bal. 3.9 7.1 1.5 0.2 0.06 0.33 0.0 86 9 Bal. 3.0 7.2 1.1 0.2 0.06 0.33 0.0 81 10 Bal. 3.0 8.2 1.4 0.2 0.06 0.33 0.0 83 11 Bal. 3.0 6.6 1.4 0.2 0.00 0.17 0.4 87

Indicated by Nos. 6-1 to 4 are samples of the copper alloys of the present invention (Bi-based alloys) and by Nos. 6-5 to 11 ate samples of the copper alloys of the present invention (Bi—Se-based alloys).

Any of these samples satisfies an index of 80% or more processible by processing equipment, with a blade and under cutting conditions for use in processing CAC406 and is found to be proccessible under substantially the same cutting conditions as for CAC406.

EXAMPLE 7 (Gap Jet-Flow Corrosion Test)

Erosion and corrosion are evaluated by means of the gap jet-flow corrosion test. The test procedure comprised mirror-polishing a test piece that had been machined to have an exposed area of 64 mm² (16 mm in diameter) relative to corrosive liquid, then jetting a test solution (a 1% cupric chloride solution) onto the exposed area part of the test piece at a rate of 0.4 t/min for five hours from a jet nozzle (nozzle diameter: 1.6 mm) disposed at a height of 0.4 mm from the surface of the test piece and measuring the maximum corrosion depth in the corroded surface.

Indicated by Nos. 7-1 to 3 shown in Table 12 are samples of the copper alloy of the present invention (Bi-based alloys) that exhibited better results than CAC406 and CAC401 shown as Comparative Examples.

TABLE 12 Maximum Sample Chemical composition value (mass %) corrosion Classification No. Cu Sn Zn Bi SE Pb P Ni depth (μm) Present Bi-based 7-1 Bal. 2.9 8.3 1.3 0.0 0.05 0.32 0.00 34.1 Invention alloy 2 Bal. 3.9 8.2 1.4 0.0 0.05 0.33 0.00 52.2 3 Bal. 3.8 6.7 1.2 0.0 0.05 0.19 0.52 46.3 Comp. CAC406 4 Bal. 4.7 5.1 0.0 0.0 4.86 0.03 0.00 64.1 Ex. CAC401 5 Bal. 2.7 9.3 0.0 0.0 4.45 0.03 0.00 84.0

EXAMPLE 8 (Tensile Test and Fracture Surface and Texture Evaluations)

The tensile test was performed in the same manner as in Example 1 (relationship between the P content and the tensile strength at 180° C.) to evaluate the tensile test pieces through the observation of the fracture surface texture, observation of the microstructure and EDX analysis.

As shown in Table 13, indicated by No. 8-1 is a sample of the copper alloy of the present invention (Bi-based alloy) containing P of high concentration, by No. 8-2 is a sample of the copper alloy of the present invention (Bi-based alloy) containing Ni to suppress the P content to within the high-concentration range (0.1<P≦0.6 mass %) and by No. 8-3 is a sample of JIS H5120 CAC911 (Bi—Se-based bronze casting), as Comparative Example, containing P in a low concentration of 0.02 mass %.

TABLE 13 Sample Chemical component value (mass %) Classification No. Cu Sn Zn Bi Se Pb P Sn Present Bi—Se-based alloy 8-1 Bal. 4.2 7.0 1.3 0.2 0.06 0.34 0.00 Invention Bi-based alloy 2 Bal. 3.9 7.0 1.3 0.0 0.06 0.15 0.43 Comp. Ex. CAC911 3 Bal. 4.4 8.0 1.4 0.2 0.04 0.02 0.00

SEM photographs and texture photographs of the facture surfaces of the alloy samples that underwent the tensile test at 180° C. are shown in FIGS. 16 to 18. In the copper alloy of the present invention, as shown in FIG. 17( b), it is observed that the central portion of the fracture surface has a fibrous texture and the peripheral portion thereof has a radial texture. In addition, as shown in FIGS. 16 and 17( a), the SEM photographs show a plurality of microscopic dimples (dents). It can therefore be considered that “ductile fracture” would occur during the tensile test at 180° C.

On the other hand, the alloy of Comparative Example, as shown in FIG. 18, assumes “cleavage” along the crystal face (cleavage surface of crystal) and no dimple can be observed from the SEM photograph. It can therefore be considered that “brittle fracture” would occur during the tensile test at 180° C.

Thus, owing to the presence of the P content in a high concentration, the strength of the alloy at the crystal grain boundaries is enhanced at a high temperature (180° C.). This indicates that the “bristle fracture” is converted into the “ductile fracture.” This is applicable to the case of containing Ni.

FIG. 19 shows the microstructure of the copper alloy of the present invention (No. 8-2), and FIG. 20 shows the distribution of the components of the alloy of FIG. 19 obtained by the EDX analysis. In the present Example, the primary crystal α is grown in a dendrite form and, in the gap thereof, a Bi-phase is observed. In the vicinity of the Bi-phase, a Cu—P compound (Cu₃P) and an Ni—P compound (Ni₃P) exist. Furthermore, since the P and Ni assume solid solutions also in the α-phase, they may possibly enhance the matrix strength.

As a result of the above evaluations, therefore, it could be supported by the observations of the fracture surfaces and textures of the samples that the presence of P content in a high concentration brought about the effect of enhancing the tensile strength at a high temperature (180° C.) and that the further presence of Ni content also brought about the effect of enhancing the tensile strength at a high temperature (180° C.) while suppressing the P content to within a high-temperature range.

INDUSTRIAL APPLICABILITY

The bronze-based alloy of low lead content according to the present invention is a copper alloy befitting various kinds of parts in a wide range of fields, including a material for plumbing instruments (valves, joints, etc.) for water supply, hot water supply or steam emission, pressure instruments (casings etc.). Since the alloy of the present invention is an alloy enhanced in tensile strength, it befits a material for parts of small wall thickness including structural members as well as the plumbing instruments. It is suitable for the process-formation of electric and mechanical products, such as gas appliances, washing machines, air conditioners, etc. Other parts and members having advantageously adopted the copper alloy of the present invention as a material for them include water contact parts, such as valves, water faucets, etc., namely ball valves, hollow balls for the ball valves, butterfly valves, gate valves, globe valves, check valves, hydrants, clasps for water heaters or warm-water-spray toilet seats, cold- and hot-water supply pipes, pipe joints, parts for electric water heaters (casings, gas nozzles, pump parts, burners, etc.), strainers, parts for water meters, parts for underwater sewer lines, drain plugs, elbow pipes, bellows, connection flanges for closet stools, spindles, joints, headers, corporation cocks, hose nipples, auxiliary clasps for water faucets, stop cocks, water-supplying, -discharging and -distributing faucet supplies, sanitary earthenware clasps, connection clasps for shower hoses, gas appliances, building materials, such as doors, knobs, etc., household electrical goods, adapters for sheath tube headers, automobile air-conditioner parts, fishing-tackle parts, microscope parts, water meter parts, measuring apparatus parts, railroad pantograph parts and other members and parts. Furthermore, the copper alloy of the present invention is widely applicable to washing things, kitchen things, bathroom paraphernalia, lavatory supplies materials, furniture parts, family room supplies materials, sprinkler parts, door parts, gate parts, automatic vending machine parts, washing machine parts, air-conditioner parts, gas welding machine parts, heat-exchanger parts, solar collector parts, automobile parts, metal molds and their parts, bearings, gears, construction machine parts, railcar parts, transport equipment parts, fodders, intermediate products, final products, assembled bodies, etc.

The following applications can be cited as intended purposes usable particularly at high temperatures.

1. <Bi-Based Alloys Containing no Ni and Bi—Se-Based Alloys Containing no Ni> (Alloys Used in Environments Requiring Not So High Resistance to Pressure)

Structural parts, such as burners, gas nozzles, flare nuts, ball taps, thermostat parts, bolts, nuts, spindles and sliding parts (bearings, gears, pushers, sleeves and worm gears).

2, <Bi-Based Alloys Containing Ni and Bi—Se-Based Alloys Containing Ni> (Alloys Requiring Strength and Resistance to Pressure:

Plumbing instruments and pressure instruments, such as heat-exchangers (plates and tubes), gas turbines, atomic furnace parts, industrial furnace parts (plumbing, valves and joints), seawater treating facilities, (plumbing, valves, containers and joints), letdown valves, electromagnetic valves, steam valves, safety valves, steam pipework, water-heating instruments, steam generators, boiler parts (plumbing, pipes, containers and joints), pump parts (casings, covers and impellers), steam traps, drainpipes, valves for steam, floats, air-conditioner parts, (plumbing, valves and joints), strainers for steam, hydraulic pump parts (casings and impellers), air release pipes, electric water heater parts (plumbing, valves and joints), hot-water containers, proportional valves, room heater parts, carburetors, service valves, ball taps, tableware washers, water contact parts for valves or water washing (ball valves, hollow balls for ball valves, butterfly valves, gate valves, globe valves, check valves, feed pipes, connecting pipes, pipe joints and strainers), headers, corporation stops, hose nipples, auxiliary clasps for water faucets, stop cocks, water-supplying, -discharging and -distributing faucet supplies and adapters for sheath tube heads.

Incidentally, though clasps or auxiliary clasps for water faucet clasps, water-feeding and hot-water feeding parts, etc. are not exposed to a temperature of 100° C. or more during ordinary use thereof, the copper alloy of the present invention is of significance under the circumferences under which cold water and hot water are alternately used or under which a high temperature of 100° C. or more by hot-air drying in a tableware washing and drying apparatus etc. is used. 

1. A bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures.
 2. A bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass %, 0.0 mass %<Ni≦3.0 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures and secure soundness of a casting.
 3. A bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass %, 0.0 mass %<Se≦1.3 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures and secure soundness of a casting.
 4. A bronze-based alloy of low lead content, comprising 2.0 to 6.0 mass % of Sn, 3.0 to 10.0 mass % of Zn, 0.1 to 3.0 mass % of Bi, 0.1 mass %<P≦0.6 mass %, 0.0 mass %<Ni<3.0 mass %, 0.0 mass %<Se≦1.3 mass % and the remainder of Cu and unavoidable impurities to improve tensile strength thereof at high temperatures and secure soundness of a casting.
 5. A bronze-based alloy of low lead content according to claim 1, further comprising 0.005 to 2.0 mass % of Pb to secure a tensile strength of at least 152 MPa at a temperature of 180° C.
 6. A bronze-based alloy of low lead content according to claim 1, that secures a tensile strength of at least 152 MPa at a temperature of 180° C. in an alloy region having a secondary dendrite spacing of 14 μm or more.
 7. A valve, water faucet clasp or water meter comprising the bronze-based alloy of low lead content according to claim
 1. 8. A bronze-based alloy of low lead content according to claim 2, further comprising 0.005 to 2.0 mass % of Pb to secure a tensile strength of at least 152 MPa at a temperature of 180° C.
 9. A bronze-based alloy of low lead content according to claim 3, further comprising 0.005 to 2.0 mass % of Pb to secure a tensile strength of at least 152 MPa at a temperature of 180° C.
 10. A bronze-based alloy of low lead content according to claim 4, further comprising 0.005 to 2.0 mass % of Pb to secure a tensile strength of at least 152 MPa at a temperature of 180° C.
 11. A bronze-based alloy of low lead content according to claim 2, that secures a tensile strength of at least 152 MPa at a temperature of 180° C. in an alloy region having a secondary dendrite spacing of 14 μm or more.
 12. A bronze-based alloy of low lead content according to claim 3, that secures a tensile strength of at least 152 MPa at a temperature of 180° C. in an alloy region having a secondary dendrite spacing of 14 μm or more.
 13. A bronze-based alloy of low lead content according to claim 4, that secures a tensile strength of at least 152 MPa at a temperature of 180° C. in an alloy region having a secondary dendrite spacing of 14 μm or more.
 14. A valve, water faucet clasp or water meter comprising the bronze-based alloy of low lead content according to claim
 2. 15. A valve, water faucet clasp or water meter comprising the bronze-based alloy of low lead content according to claim
 3. 16. A valve, water faucet clasp or water meter comprising the bronze-based alloy of low lead content according to claim
 4. 17. A valve, water faucet clasp or water meter comprising the bronze-based alloy of low lead content according to claim
 5. 18. A valve, water faucet clasp or water meter comprising the bronze-based alloy of low lead content according to claim
 6. 